Oversize Piston Kits...

Now that I finally have my bike running good and leak free, I'm lining up some more upgrades for this winter.

First on the list is some bigger pistons. I have heard that for street use, a big block is a no-no as there are no cooling passages between the cylinders which leads to overheating. Therefore i have decided on 1197cc which i think is the biggest you can get out of the stock block.

It looks like I have 2 choices: MTC or Wiseco. Which is better and where is the best place to get a good price on these babies?

Other coming upgrades: dry-blocking, oil cooler, welded crank, better ignition system (with a digital advance - I'm fed up with the mechanical advance).

-Dave

Dave
you might as well weld crank and have trans looked at first. also do you plan on installing new sleeves ? what are we working on Z1 900 KZ1000 J MODEL GPZ1100 ? i have seen this all to many times my new customers had a bore kit installed then come to me with twisted crankshaft or a trans popping out of gear.

You will have just as many heat problems if not more with the 1200 kit as you would have with a big-block. You will be at the extremes on both the sleeve wall thickness and the block thickness also. There wont be enough metal there to dissipate the heat for any kind of stop and go traffic. You will be fine on the highway but if you ketch any kind of traffic you will be in trouble. I like the MTC pistons because they use and come with buttons and not clips. If you use the Wiseco pistons they are also good but I would use MTC buttons with them.

I don't understand how a thin wall causes overheating. It's all about heat transfer. I'm not just using the mass of the block to absorb the heat, I'm using it to transfer heat to the fins. Where am I thinking wrong on this?

Why are buttons better than clips? I have never but NEVER seen a clip come out that was new when installed and installed properly.

-Dave

Also, when I tore my engine down last winter, I inspected the trans. The dogs are OK, but that's all. Not sharp, a little rounded even. It NEVER jumps out of gear.

I have a spare crank that I will be sending out to be trued/balanced/welded, so no worries there. I don't do drag-race starts or slam it into gear or anything like that so I'm not to worried about twisting the crank until then.

Did I mention that the bike runs GREAT and I'm probably a fool for continuing to mess with it?

-Dave

beefsquasher wrote:

I don't understand how a thin wall causes overheating. It's all about heat transfer. I'm not just using the mass of the block to absorb the heat, I'm using it to transfer heat to the fins. Where am I thinking wrong on this?

Why are buttons better than clips? I have never but NEVER seen a clip come out that was new when installed and installed properly.

-Dave

Don't think he's saying the thin wall create the heat - the large piston and compression ratio creates the heat. I also think he's saying that a 1200cc overbore has similar heat issues on the street to a big bore motor in the real world. But then, I'm interpreting and could be wrong.

Hey I used to build a new small block every winter for my Camaro.
I found "If you want to play then you got to Pay" when it comes to HP.
But on topic, I would think that the thinner the sleeve, then the more likely to distort, city stop and go on a hot day? It will be easier no doubt, will it? Well if you build it and at 5000mi you start getting blow-by, then I say it most likely did.
We used to take some of the VW air cooled motors out to 94mm, stock was 82mm. Press on barrel stiffeners were the only way to go, and that a lot more machining, cutting down fins to add the stiffeners.

beefsquasher wrote:

Did I mention that the bike runs GREAT and I'm probably a fool for continuing to mess with it?

-Dave

Yeah, I wasn't going to bring that up, but since you did..... to actually take advantage of the bigger pistons you would need to port and polish the intake and increase carb size to feed them, and get exhaust headers that are low enough restriction to let all that breathe. Bike engines come from the factory with all the parts pretty well tweaked up for best HP, changing only one variable won't get optimum performance. My two cents for whatever it's worth these days.

DoubleDub wrote:

beefsquasher wrote:

I don't understand how a thin wall causes overheating. It's all about heat transfer. I'm not just using the mass of the block to absorb the heat, I'm using it to transfer heat to the fins. Where am I thinking wrong on this?

Why are buttons better than clips? I have never but NEVER seen a clip come out that was new when installed and installed properly.

-Dave

Don't think he's saying the thin wall create the heat - the large piston and compression ratio creates the heat. I also think he's saying that a 1200cc overbore has similar heat issues on the street to a big bore motor in the real world. But then, I'm interpreting and could be wrong.

Not wrong, I think that's exactly right. The extra bore draws more fuel/air mix, so there is more heat generated at combustion. Basically same heat transfer system being fed more heat to try to get rid of = higher operating temps.

beefsquasher wrote:

I don't understand how a thin wall causes overheating. It's all about heat transfer. I'm not just using the mass of the block to absorb the heat, I'm using it to transfer heat to the fins. Where am I thinking wrong on this?

You are thinking right but forgetting the bigger bore will generate more heat to be transferred to the air.

If it is a 1000 block, 1260 is the limit. Keep the cylinder pressure down with overlap, and you should be OK.
Here is your piston selection. kzzone.com/pistons.html

leave the pistons alone.
buy some cams like .429 and it will be a different beast.
for what you all ready have with the 1075 kit and flatslides you undercammed for the power you want.
there is a member here who had a 1200 with .410 cams and 36's and a 1075 with .429's and 34's walked away from him most times.
these motors are all about the cams, not piston size.